Suppose you have a program consisting of just >. What happens to it when you run your code:

  1. s/>/\t\t++k;\n/g; transforms it into \t\t++k;\n
  2. s/</\t\t--k;\n/g; does nothing, it's still \t\t++k;\n
  3. s/\+/\t\t++*k;\n/g; transforms each + present in the program into \t\t++*k;\n, leaving you with \t\t\t\t++*k;\n\t\t++*k;\nk;\n
One way to solve it would be to create a hash of all possible replacements: 
my %sub = {
 ">" => "\t\t++k;\n",
 "+" => "\t\t++*k;\n",
 ... # fill as needed
}

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Then run the substitution only once, on each symbol: 
s/(.)/$sub{$1}/ge

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Fixing the warnings about undefined hash elements (when do they happen?) and/or constructing a regular expression that would only match brainf*ck characters is left as an exercise for the reader.

A faster, but less elegant solution would be to replace + and - first, then consider other characters which might produce their own [+-].

In reply to Re: Weird substitution, missing output by Anonymous Monk
in thread Weird substitution, missing output by timpoiko

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